Unable to fix hum on my F5 - diyAudio
Go Back   Home > Forums > Amplifiers > Pass Labs

Pass Labs This forum is dedicated to Pass Labs discussion.

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 8th April 2011, 01:23 PM   #1
anilva is offline anilva  India
diyAudio Member
 
Join Date: Mar 2004
Location: Bangalore
Default Unable to fix hum on my F5

Wanted to originally post this as a part of F5 thread, but thought it would be lost in 1000s of posts there.

My problem is with a recently built F5 using CViller ver 2.0 boards and running dual output pairs of Toshibas.

The build is stock F5 schematic except the outputs. Even the wiring is as per the original FW F5. This has worked well for my other F5 builds. No problem.

Now I have a slight hum in both the channels of F5 with the input signal shorted. I tried lot of things and finally managed to reduce the hum by nearly half, by soldering two 220uF electrolytics on the F5 PCB across the power rails. But there is STILL hum.

I tried shielding the toroid with a sheet steel barrier, but no difference.

The power supply is a standard Pass PS with 4 * 15000 uF on each rail in a CRC config.

I have tried lifting the ground from the chassis/electrical earth, but no change.

Clearly by adding few caps on the PCB, there is a improvement. What else can be done. Should I add a small nano/pico cap as well along with 220uF? The hum seems to be getting picked up at the PCB location, or through the power rail wiring to the PCB.

Here are the images (before adding the caps at the PCB):


Click the image to open in full size.
Click the image to open in full size.
Click the image to open in full size.
Click the image to open in full size.
Click the image to open in full size.


Thanks in advance.
__________________
DIY F5, F5T, F6, Aleph J, Fostex 206 based BLH, Altec Onken with 515B LF & 288H HF, Technics SP10 MKII & EMT938 turntables
  Reply With Quote
Old 8th April 2011, 02:09 PM   #2
Zen Mod is offline Zen Mod  Serbia
diyAudio Member
 
Zen Mod's Avatar
 
Join Date: Jan 2003
Location: ancient Batsch , behind Iron Curtain
pictures are dead thumbnails

anyway , few tips without seeing details -you can try to rotate toroid

also - you can try to displace toroid from the box ( extend wires temporary) to be sure that hum isn't magnetically induced
if nothing of that helps , buy some caps

serious ones - 10mF upwards
__________________
my Papa is smarter than your Nelson !
clean thread; Cook Book;PSM LS Cook Book;Baby DiyA ;Mighty ZM's Bloggg;Papatreasure;Papa... by Mighty ZM
  Reply With Quote
Old 8th April 2011, 03:20 PM   #3
anilva is offline anilva  India
diyAudio Member
 
Join Date: Mar 2004
Location: Bangalore
Quote:
Originally Posted by Zen Mod View Post
pictures are dead thumbnails

anyway , few tips without seeing details -you can try to rotate toroid

also - you can try to displace toroid from the box ( extend wires temporary) to be sure that hum isn't magnetically induced
if nothing of that helps , buy some caps

serious ones - 10mF upwards
Sorry. Will post the pictures again.

Have tried turning the toroid. No difference. Have not tried removing the toroid out of the box. When you say 10 mF, you mean 100000 microfarad isn't it?
__________________
DIY F5, F5T, F6, Aleph J, Fostex 206 based BLH, Altec Onken with 515B LF & 288H HF, Technics SP10 MKII & EMT938 turntables

Last edited by anilva; 8th April 2011 at 03:44 PM. Reason: typo error
  Reply With Quote
Old 8th April 2011, 03:42 PM   #4
anilva is offline anilva  India
diyAudio Member
 
Join Date: Mar 2004
Location: Bangalore
Here are the pictures:
Attached Images
File Type: jpg IMG_6972.JPG (228.4 KB, 296 views)
File Type: jpg IMG_6973.JPG (212.3 KB, 288 views)
File Type: jpg IMG_6975.JPG (260.8 KB, 258 views)
__________________
DIY F5, F5T, F6, Aleph J, Fostex 206 based BLH, Altec Onken with 515B LF & 288H HF, Technics SP10 MKII & EMT938 turntables
  Reply With Quote
Old 8th April 2011, 03:49 PM   #5
diyAudio Member
 
jackinnj's Avatar
 
Join Date: Apr 2002
Location: Llanddewi Brefi, NJ
First question -- when you short the inputs, does it still hum?

Second -- I would route the input cable along the side of the chassis and away from the filter caps. Consider using shielded twisted pair, not coax, and connect the shield on the amplifier side.

Third -- You might want to consider a ground loop breaker if the above don't work.
  Reply With Quote
Old 8th April 2011, 04:05 PM   #6
AndrewT is offline AndrewT  Scotland
diyAudio Member
 
Join Date: Jul 2004
Location: Scottish Borders
Is that 8 mosFETs attached to those heatsinks?
How many F5s are in there.

+-60mF should get ripple low enough?

Turn the bias down to 100mA. Does it still hum?
How much hum, measure it?

It is almost certainly a wiring fault.
__________________
regards Andrew T.
  Reply With Quote
Old 8th April 2011, 05:36 PM   #7
anilva is offline anilva  India
diyAudio Member
 
Join Date: Mar 2004
Location: Bangalore
Quote:
Originally Posted by jackinnj View Post
First question -- when you short the inputs, does it still hum?

Second -- I would route the input cable along the side of the chassis and away from the filter caps. Consider using shielded twisted pair, not coax, and connect the shield on the amplifier side.

Third -- You might want to consider a ground loop breaker if the above don't work.
Ok. Will change the input wire from coax to twisted pair with a shield.

I have heard about ground loop breaker but do not know what it is exactly.

Quote:
Originally Posted by AndrewT View Post
Is that 8 mosFETs attached to those heatsinks?
How many F5s are in there.

+-60mF should get ripple low enough?

Turn the bias down to 100mA. Does it still hum?
How much hum, measure it?

It is almost certainly a wiring fault.
Andrew, this is a dual output pair per channel. Therefore there are 4 mosfets on each channel.

Will check with 100mA of bias. I cannot see any wiring fault. I have made couple of F5s before with the same wiring topology and they are dead silent.

Thanks.
__________________
DIY F5, F5T, F6, Aleph J, Fostex 206 based BLH, Altec Onken with 515B LF & 288H HF, Technics SP10 MKII & EMT938 turntables
  Reply With Quote
Old 8th April 2011, 05:38 PM   #8
anilva is offline anilva  India
diyAudio Member
 
Join Date: Mar 2004
Location: Bangalore
Quote:
Originally Posted by AndrewT View Post
Is that 8 mosFETs attached to those heatsinks?
How many F5s are in there.

+-60mF should get ripple low enough?

Turn the bias down to 100mA. Does it still hum?
How much hum, measure it?

It is almost certainly a wiring fault.
How do I measure hum? Ac at the output?
__________________
DIY F5, F5T, F6, Aleph J, Fostex 206 based BLH, Altec Onken with 515B LF & 288H HF, Technics SP10 MKII & EMT938 turntables
  Reply With Quote
Old 8th April 2011, 05:46 PM   #9
diyAudio Member
 
Bksabath's Avatar
 
Join Date: Dec 2007
Anilva
maybe you have a bunch of wires running to close and parallel to each other.

Could you trim the excess off and keep suply output and imput avay from eah other and crossing at 90.
  Reply With Quote
Old 8th April 2011, 06:26 PM   #10
diyAudio Member
 
bobodioulasso's Avatar
 
Join Date: May 2008
If you draw twice as much current as standard F5 you need more filtering caps.
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
F5 hum preiter Pass Labs 10 3rd June 2012 02:10 PM
F5 Cascoded - an alternative for my interest in the Balanced F5 NYCOne Pass Labs 159 24th March 2011 06:23 AM
Perpetuum-Ebner PE66: To fix or not to fix... Grendel the Cat Everything Else 0 6th April 2007 06:37 AM
Tivoli Model1 PSU hum fix / upgrade? jives11 Solid State 1 24th May 2004 09:30 AM


New To Site? Need Help?

All times are GMT. The time now is 05:46 PM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2